Drillability and mechanical parameters of laser hot cracking sandstones

Over recent years, shallow coal resources that can be easily mined have been gradually exhausted. As a result, conventional drilling techniques tend to face challenges such as low rock-breaking efficiency, high drilling costs, and environmental pollution in the exploration and exploitation of deep coal resources. Therefore, there is an urgent need to introduce a new auxiliary rock-breaking technique for drilling. Focusing on the new laser-assisted rock-breaking technology, this study systematically conducted mechanical and drillability tests on sandstones after laser irradiation for different durations, aiming to explore the temporal and spatial evolution of the temperature field of hard sandstones, the propagation of cracks on the sandstone surfaces, and the mechanical parameters and drilling efficiency of sandstones under laser irradiation. The results are as follows. (1) With an increase in laser irradiation time, the number of cracks on the sandstone surface gradually increased from two to five, with the cracking area increasing from 6.78 mm² to 36.85 mm². (2) The evolution of the temperature field exhibited the Gaussian distribution, presenting a circular decrement from the hot-melt zone to the low-heat zone. After 15 s of laser irradiation, the thermal equilibrium was reached, with the evolution of the temperature field tending to be stabilized. (3) After 50 s of laser irradiation, the compressive strength and elastic modulus of sandstones decreased by up to 74.6% and 92.7%, respectively, and the axial peak strain increased from 0.52% to 1.65%. These results indicate that sandstones shifted from an elastic state to a semiplastic/plastic state after laser irradiation. (4) After 50 s of laser irradiation, the penetration rate of sandstones increased from 0.09 mm/s to 4.30 mm/s, and the weight loss ratio increased from 2.73% to 27.36%. (5) Appropriately setting laser parameters could improve rock-breaking efficiency and reduce drilling costs. The penetration rate and weight loss ratio of sandstones increased the most after 20 s of laser irradiation, when fast and economical rock-breaking could be achieved. This study preliminarily demonstrates the efficiency and feasibility of the laser-assisted rock-breaking technique, thus providing a theoretical basis for efficient rock-breaking in deep drilling.